1. Field of the Invention
The present invention is directed to a method for defining at least one parameter in a RLC discharge circuit during the output of an electrical pulse to biological tissue, and to an apparatus for the implementation of the method, of the type having a storage capacitor and a coil which can be connected via biological tissue to form an RLC discharge circuit to which a measuring means having an evaluation circuit is coupled.
2. Description of the Prior Art
A method and an apparatus of this type are known from the periodical Medical Electronics, October 1986, pages 156-158 and are set forth therein in combination with a defibrillator. For medical as well as legal reasons, a measurement and subsequent documentation of the critical parameters present upon the output of an electrical pulse for defibrillation in the discharge circuit are required. The resistance of the biological tissue, for example, the patient resistance, the energy stored in the charging capacitor (storage capacitor), as well as the energy that results from these two parameters and is supplied to the patient (living biological tissue) are all commonly used as variable parameters. In the above known apparatus, a measuring means is connected via a current transformer to an RLC discharge circuit for the definition of such parameters. The discharge current (the output electrical pulse) flows through the primary side of the current transformer. The secondary side of the transformer is loaded with a load resistor and is connected to the measuring means. The measuring means is fashioned such that the maximum value of the secondary voltage of the transformer is measured and is evaluated in a microprocessor for identifying the patient resistance.
Consequently, the precision of this measuring method is dependent on the magnitude of the amplitude of the secondary voltage of the induced current. Leaving the voltage ratio of the transformer, the capacitance of the charging capacitor and the inductance of the coil as well as the resistance thereof (fixed parameters) out of consideration, the amplitude is dependent on two variable parameters. One variable parameter is the patient resistance to be identified and the other variable parameter is the energy that is regularly adjustable and stored in the charging capacitor. For identifying the patient resistance, thus, it is necessary to define the energy stored in the charging capacitor and to simultaneously take the amplitude of the secondary voltage into consideration in the evaluation of the measured quantity. This is complicated and, above all else, leads to more pronounced measuring tolerances.